Anaesthesia Maintenance Flashcards
What should be done when intubating?
Sufficient depth of anaesthesia - eyes rotated ventrally, minimal, sluggish palpebral reflex, loose haw tone, no swallowing reflex on stimulation
Pull tongue out and use laryngoscope - don’t touch epiglottis or larynx
Visualise laryngeal opening
Local anaesthesia
Lubrication
How do you measure for endotracheal tube size?
Measure from mouth to point of shoulder
Describe some problems that can occur with endotracheal tubes
Occlusion of end of ET tube - can be prevented with Murphy’s eye
Endobronchial intubation
Compression of inside of tube
Stretching of tracheal wall
Mucus in tube - risk of occlusion and infection
Describe intubation in cats
Spray larynx with local anaesthetic - desensitise, reduce laryngospasm during intubation
Intubease - lidocaine spray
Easy to overdose - take care of local anaesthetic toxicity
Alternative options - V-gel, laryngeal mask
What six things are involved in balanced anaesthesia
Minimization of stress Analgesia Muscle relaxation Decrease amount of drugs used Minimize autonomic reflex activity Unconciousness
What two things are dose-dependent with anaesthetic agents?
Cardiovascular depression - decrease in cardiac output, vasodilation, reduced blood pressure
Respiratory depression - decreased respiratory rate, decrase tidal volume, reduced minute volume
What do most general anaesthetics not provide?
Analgesia
What is the one anaesthetic that does provide analgesia?
Ketamine
Why is analgesia still required when patient is unconscious?
Prevent upregulation of pain processing pathways
What are the four common routes of anaesthesia administration?
Inhalational
Intravenous - TIVA, intermittent boluses, CRI
Combination of injectable and inhalational - balanced techinques, PIVA
Intramuscular - single sufficient, darting wild or zoo animals
What are four examples of injectable anaesthetics?
Propofol
Alfaxalone
Ketamine
Thiopental
What are six examples of inhalational anaesthetics?
Isoflurane Sevoflurane Halothane Desflurane Nitrous oxide Xenon
What is the one inhalational agent that isn’t administered and removed by the lungs?
Halothane
How do inhalational anaesthesia agents work?
From alveoli
Agent absorbed into blood
Travel up to brain
Induce effects
Where can inhalational agents redistribute?
Into other tissues - fat
Fat solubility may slow recovery from long anaesthetic
What factors affect inhalational agent uptake?
Pressure gradient from vaporizer to brain - vaporizer, anaesthetic circuit, alveoli, blood, brain
Brain concentration approximates alveolar concentration
What factors affect the speed of induction?
High partial pressure in lungs equals high partial pressure in brain
Agents soluble in blood will have lower partial pressure in lungs - lower partial pressure in brain
Speed of induction slower for more soluble agents - also recovery
Describe the blood/gas partition coefficient
Number of parts of gas in blood vs. alveolus
High number means gas is very soluble in blood
More soluble agents are slower to change depth of anaesthesia during maintenance
Give the five main inhalational agents in decreasing partition coefficient
Halothane Isoflurane Sevoflurane Nitrous oxide Desflurane
What is the MAC?
Minimum alveolar concentration - amount required to prevent movement in response to pain in 50% of animals
What concentration should be aimed for in clinical anaesthesia?
1.25-1.5 times MAC
What does the MAC depend on?
Other agents also administered
Species
What factors influence MAC?
Decreases - hypothermia, very young, older, severe hypoxia/hypercapnia, severe hypotension, CNS depressant drugs, pregnancy
Increases - hyperthermia, young, fit, excitation
What is MAC not affected by?
Length of anaesthesia
Gender
Blood pH
Give MAC values for the dog, cat and horse with isoflurane and sevoflurane
Dog - isoflurane 1.3, sevoflurane 2.3
Cat - isoflurane 1.6, sevoflurane 2.6
Horse - isoflurane 1.3, sevoflurane, 2.3
What are the differences and similarities with anaesthetic agents?
Cardiovascular depression leading to reduced blood pressure - mainly with halothane, some with iso/sevo
Respiratory depression - similar for all
Liver metabolism - around 20% in halothane, lower in others
Describe sevoflurane metabolism
Theoretically free fluoride ions released - toxic to kidney, though no problems reported clinically
Compound A formed during reaction with hot and dry carbon-dioxide absorber - nephrotoxic, newer absorbers prevent this
Low flow anaesthesia potentiates these processes
Describe isoflurane
Vasodilation CV depression Cheaper Stronger smell Patient less compliant
Describe sevoflurane
Less CV side effects than Iso Maintains cerebral perfusion better than Iso More expensive Better tolerated Less irritant Compound A - reaction with CO2 absorbant
Describe Nitrous oxide
MAC in animals around 200%
Cannot be used as sole agent - hypoxia
Mild analgesic properties
Very insoluble
Very fast onset
Can speed onset of another agent - second gas effect
Less important now that insoluble agents are routinely used
Need diffusion hypoxia at end of anaesthetic - diffuses rapidly into lungs, reduces partial pressure of oxygen in lungs
Health risk with long term exposure
Atmospheric pollution
When does most aneasthetic mortality occur?
Recovery period
When should extubation be done?
When swallowing reflex returns
Cats slightly earlier to prevent laryngospasm
Later if concerned about airway protection - brachycephalic dogs, vomiting risk, ruminants
What should be done doing recovery?
Continue monitoring - heart rate, respiratory rate, temperature
Oxygen administration if necessary
Fluid therapy if necessary
Temperature
Post-operative analgesia
Nursing care and TLC - empty bladder, comfortable bandages
What are the main goals with anaesthesia monitoring?
Make sure all components of balanced anaesthesia are provided for
Maintain homeostasis as best as possible
Detect any adverse effects of anaethesia
What should you try and adopt when monitoring?
Methodical, structured way of monitoring
Patient - monitoring equipment - anaesthetic machine - fluids
What should be logged on an anaesthetic record?
Time, dose and route of drugs given
All intra-operative monitoring every 5 minutes
Iv fluids given - rate, type
All procedures performed
Time of important events - induction, positioning, start of surgery, extubation
Unusual events or complications
Condition of animal at the end of the procedure
How can blood volume be calculated with dogs and cats?
80ml/kg for dogs
60ml/kg for cats
When should we note blood loss?
When it is equal to 10%, 15% and 20% of blood volume
Helps decision making on whether crystalloids, colloids or blood are likely to be needed
What should be clinically observing when monitoring anaesthesia?
Depth of anaesthesia Mucous membranes Pulse Chest movements Pupil size Response to surgery Blood loss Urine output
What should we be using monitoring equipment to monitor during anaesthesia?
Respiratory gases Pulse oximeter Blood pressures ECG Thermometer Blood gases
Why is it important to check cylinder pressure and oxygen flow meters constantly?
Some machines may not have low oxygen warning alarms fitted
How can you ensure you are not delivering an hypoxic mixture to the patient?
Check oxygen/nitrous oxide ratio on a regular basis
Only really necessary when using nitrous oxide
What things should be monitored on the equipment during anaesthesia?
Cylinder pressure Oxygen flow meters Oxygen/nitrous oxide ratio Vaporizer settings Level of volatile anaesthetic in vaporizer Breathing system - operation, disconnection Rate of fluid administration Contents of fluid bags
How does monitoring equipment help with anaesthesia?
More detailed information
Early warnings
Helps reduce morbidity and mortality
How can we assess the depth of anaesthesia?
Cardiovascular responses to stimulation - heart rate, blood pressure Respiratory changes - rate, tidal volume Eye position Nystagmus Lacrimation Pupil size Response to light Neurological responses - cranial nerve reflexes, other reflexes Muscle relaxation EEG changes
What physiological parameters do we continually assess in anaesthesia patients?
Heart rate
Pulse - rate and quality
Respiration - rate, character, quality
All particularly in response to painful stimuli
What is a simple way to monitor the heart and breathing?
Oesophageal stethoscope - inexpensive, non-invasive
What does a capnograph do?
Measures CO2 in respiratory gases
Continuous
Non-invasive
How does a capnograph estimate partial arterial pressure?
End tidal carbon dioxide
Approximately partial arterial carbon dioxide
What are the normal ranges for end-tidal CO2?
35-45 mmHg
Values greater than 60 mmHG may warrant IPPV
What do increased end-tidal CO2 indicate?
Alveolar hypoventilation
Increased cardiac output
Hyperthermia
Bicarbonate administration
What do decreased end-tidal CO2 indicate?
Decreased cardiac output
Hyperventilation/shallow breaths
Artefact
Hypothermia
What does anaesthetic agent concentration measure?
Inspired and expired concentrations
Helps in assessing depth
Need to know MAC of different agents
Useful when using very low flows in a circle system
How can we assess oxygenation?
Clinically - cyanosis
Arterial blood gas analysis - intermittent results, invasive, possible complications
Pulse oximetry - continuous, non-invasive, measured at level of arterioles
What does pulse oximetry give information on?
Arterial haemoglobin saturation
Pulse rate
Adequacy of tissue perfusion
Why is saturation important?
Nearly all oxygen in blood is carried in combination with haemoglobin
Measurement of saturation enables estimation of oxygen content and oxygen delivery to tissues
Oxygen delivery equals oxygen content times cardiac output
What is the normal SpO2 range?
95-100%
SpO2 less than 90% means a PaO2 less than 60mmHg
PaO2 less than 60mmHg defined as hypoxaemia
What is pulse oximetry not a good measure of?
Ventilation
When should you keep the pulse oximetry probe in place?
Until you know SpO2 can be maintained on air
What should be done if SpO2 is low on 100% O2?
Check if value is true - check oxygen supply, check probe position, check BP, have you used an alpha-2 agonist?
What is happening if SpO2 is low on 100% O2 and the value is true?
Increased right to left shunting of blood - anatomical, inrapulmonary
Impaired diffusion - very rare
What does an ECG provide information on?
Electrical activity of the heart
Doesn’t tell us about - cardiac output, blood pressure, mechanical activity of the heart
What is arterial blood pressure used to assess?
Adequacy of tissue perfusion - O2 delivery
What may hypotension be due to?
Reduced CO
Reduced SVR
Commonest cause is reduced CO due to anaesthetic drugs or hypovolaemia
What are the normal arterial BP values?
Systolic 100-160mmHg
Diastolic 60-100mmHg
Mean 80-120mmHg
What value should arterial BP be kept above?
60-70mmHg otherwise renal perfusion will fall
Describe a Doppler ECG
Accuracy dependent on cuff size
Cuff about level with heart
Measures systolic BP
Cats - value is between systolic and mean
Some recommend adding 14mmHg in cats for true systolic BP
Describe oscillometry
Accuracy dependent on cuff size Cuff about level with heart Gives SAP, MAP and DAP Tends to under-read MAP value is most accurate
What should be done with invasive BP if blood pressure is low?
Keep mean BP above 60-70mmHg
Otherwise renal perfusion will fall
What shuold be done - reduce depth, fluid bolus, inotropes, avoid NSAIDs
When are blood gases monitored?
If concerns about lung function during anaesthesia
What can be gained from an arterial sample of blood gases?
Efficiency of ventilation
What can be gained from venous samples of blood gases?
Acid-base status
What infromation is given by blood fases?
PO2 PCO2 pH Oxygen saturation HCO3- BE Electrolytes
What does arterial O2 tension (PaO2) measure?
How well the lungs can oxygenate blood
What is arterial CO2 tension (PaCO2) a measure of?
Alveolar ventilation
What are the upper limits of PaCO2?
Values greater than 60 mmHg - may warrant IPPV
How is core temperature most effectively measured?
Thermistor probe-oesophagus, rectum
What patients are more at risk of hypothermia?
Smaller patients - increased surface area to body mass ratio
